An electromagnetic type horn apparatus is mounted in a front side of a vehicle such as automotive vehicle. As one example, an electromagnetic type horn apparatus for resonating a sound generated by vibrations of a diaphragm with a resonator is known. Such a horn apparatus provided with a resonator is described in, for example, Japanese Patent No. 5058912 (FIG. 1). The horn apparatus described in Japanese Patent No. 5058912 (FIG. 1) is provided with a case having a bottomed tubular shape, an electromagnet (a coil and a fixed iron core) provided in the case, a diaphragm provided so as to close an opening of the case, a movable iron core which vibrates the diaphragm, and a cover provided on an outer surface of the diaphragm and forming an air vibrating chamber in the case. In addition, a sound emitting opening is provided at a central part of the cover, and a resonator is disposed to be opposed to the sound emitting opening. As a result, the sound generated by the vibrations of the diaphragm passes through inside of the resonator to resonate and is then emitted to outside the resonator.
However, according to the horn apparatus described in Japanese Patent No. 5058912 (FIG. 1), as shown in FIG. 11 which is a partial enlarged view of a conventional horn apparatus, a setting hole “f” of a diaphragm “e” is swage-fixed to a setting portion “b” of a movable iron core “a” via a first washer “c” having a large diameter and a second washer “d” having a small diameter. Therefore, the cross sectional shape of a sound emitting opening “g” and an annular air flow channel “h” is formed between the washers “c” and “d”, and becomes a stepped shape having vertical surfaces “k” which disturbs a smooth air flow between an air vibrating chamber “m” and a resonator “n”. Therefore, the horn apparatus encounters a problem that disturbance of air flow is easily generated during operations and variations are easily generated in acoustic characteristics.